The typical test for measuring the crack growth rate of a notched specimen tested in accordance with ASTM test method E647-88, volume 03.01 of the 1988 ASTM Standards requires a significant amount of time with the use of costly testing equipment. Materials typically used in aircraft engines usually require two to three weeks or longer to perform the 3-point-bend specimen crack growth test. Obviously, in the development process of new alloys, it would be an advantage to be able to screen the new alloys over a shorter period of time using less costly test machinery.
I have found that I can obtain an indication of whether or not a specimen has the likelihood of meeting success by subjecting the specimen to a constant load either under the temperatures in which the material is intended for ultimate use or under standard day or ambient conditions. The test equipment consists of a relatively inexpensive fixture, motor driven eccentric for cyclically displacing a load over a constant distance and recording the load level with a standard 4 arm bridge load cell. This allows one to ascertain and calculate a single point of the .DELTA.K (stress intensity) and compare the results with the stress-intensity factor range versus the crack growth rate (da/dn) which is indicative of the material's resistance to stable crack extension under cyclic loading.
This type of screening that discounts the specimens that are unlikely to succeed saves time, and would allow better utilization of the more expensive equipment for standardized 3-point crack growth testing would realized.
Furthermore, it is contemplated that this testing equipment could be operated by personnel without having to expend a great amount of training.